CASE



Case

Case

QUESTION 1

Arsenic and lead can be simultaneously reduced to the hydrides in hydrochloric acidnitroso R salt and hydrochloric acid-potassium ferricyanide media by means of sodium tetrahydroborate( III) reduction. The latter is preferable owing to the fact that lower detection limits for both arsenic and lead can be obtained by inductively coupled plasma-atomic emission spectrometry in combination with hydride generation.

It is well known that hydride generation, especially plumbane generation, is subject to interferences from transition metals and hydride forming elements. Further work on developing an understanding of these interferences occurring in the recommended media and on the way to eliminate these interferences will be necessary before the technique can be applied to analyze real samples with complex matrices. It is very likely that better detection limits would be obtained if a superior gas-liquid separator were used, or, as a reviewer has suggested, an axially viewed ICP system.

Arsenic, arsenic trioxide and pentoxide, arsenous acids, arsenic acid and their salts (arsenites and arsenates) are carcinogenic substances (Carcinogen category 1) and do not, therefore, have MAK and BAT values (Greim 2002:15). The former TRK value (technical exposure limit) for arsenic and its inorganic compounds was 0.10 mg arsenic/m3 (measured as the inhalable fraction of the aerosol; calculated as arsenic). This arsenic concentration in air correlated with an arsenic concentration in urine of 130 µg/l at the end of exposure or the end of the shift after several previous shifts (see the EKA documentation for arsenic trioxide in Volume 2 of this series; Greim and Lehnert 1995:11). The inorganic arsenic and methylated metabolites are analysed together.

QUESTION 2

The contents of arsenic and lead in the environment is of great concern because both of them are recognized as cumulative poisons to animals and people. In addition, arsenic has been identified as a potential human carcinogen. Therefore, determination of trace arsenic and lead in various samples is of great interest of analysts and environmental chemists.

Among the various techniques, inductively coupled plasma-atomic emission spectrometry (ICP-AES) is favored because of its capability for multi-element analysis. However, the sensitivity of ICP-AES by solution nebulization cannot meet the needs of determining As and Pb at low trace and ultra-trace concentrations. The combination of ICP with mass spectrometry does provide excellent detection limits for arsenic and lead of less than 1 ng/ml, ~ but the expense of such equipment has prevented their being commonplace in analytical laboratories.

Since Thompson and co-workers combined ICP-AES with hydride generation 2 in 1978, this technique has received considerable attention by analysts because the sensitivity and detection limit could be greatly improved, compared to those obtained by conventional solution nebulization into an ICP source. Thus, methods of sequential or simultaneous determination of hydride forming elements, 3 and simultaneous determination both hydride forming elements and non hydride forming elements 45 have been developed. Nevertheless, it is difficult to find reasonable compromise conditions required for the simultaneous determination of all eight of the hydride forming elements because of their different requirements for hydride ...